All that said, I'm struggling to see the good side of Apple's decision to remove the 3.5mm jack. It'll make the phone worse in daily use for me - I won't be able to sit at my desk all day and charge my phone while listening to my existing, good headphones.
There are no winners in this game except for Apple, which can push more licenses and proprietary accessories.
There are valid product reasons for moving away from the 3.5mm jack though, like adding a power line that allows you to make active noise-canceling headphones that don't require their own battery, or outputting to more than two (stereo) speakers over a single cable.
And there's no line-out, so you're effectively dual-amping any signal if you use an amplifier on the built-in 3.5mm jack.
In any case, I think they should have kept the onboard jack, and people who really care would continue to use external DAC/Amp stacks.
There is no need to lock consumers into one way or another when there are already phones that can handle either!
You could already connect an off-board DAC to the iPhone pre-iPhone 7
Put differently, when the DAC is in the phone, you need to worry about two things in order to get good sound quality — the quality of the headphones and the quality of the phone. With a DAC in the headphone, you worry about only one.